1. Field of the Invention
The present invention relates to a sputtering target (hereinafter, it will be referred to as a target) having excellent resistance to cracking, used for forming a ZrO2—In2O3 based protective film for an optical storage medium, the optical storage medium being capable of recording, playing, both of recording and playing, or deleting information using a laser light.
This application claims priority from Japanese Patent Application No. 2007-231670 filed on Sep. 6, 2007, the contents of which are incorporated herein by reference in their entirety.
2. Background Art
Generally, a ZnS—SiO2 based protective film has been known as a typical protective film (the protective film includes a lower section protective film and an upper section protective film) constituting an optical storage medium such as an optical disc. The ZnS—SiO2 based protective film has component compositions including 20% of silicon dioxide (SiO2) and the rest thereof constituted of zinc sulfide (ZnS).
It is known that the ZnS—SiO2 based protective film having the foregoing component compositions are obtained by sputtering, by use of a ZnS—SiO2 based target made of a hot-pressed sintered body including 20% of silicon dioxide (SiO2) and the rest thereof constituted of zinc sulfide (ZnS).
However, in the ZnS—SiO2 based protective film that is obtained by sputtering, by use of the ZnS—SiO2 based target, S of ZnS diffuses to a storage film caused by reiteration of rewriting the storage film and irradiating the storage film with a laser light, there is a drawback in that the performance of reiteration of rewriting is degraded.
As a result, development of a protective film without S progresses. As an example of a protective film without S, a ZrO2—In2O3 based protective film for an optical storage medium has been proposed. The ZrO2—In2O3 based protective film includes zirconium oxide and indium oxide as main components, and component compositions made of ZraInbAcO100-a-b-c in which an oxidative product of the A (SiO2, Cr2O3, Al2O3, CeO2, TiO2, SnO2, or the like) is included, where “A” represents one, two, or more of Si, Cr, Al, Ce, Ti, and Sn, “a” represents an amount greater than 5 atomic percent and less than 23 atomic percent, “b” represents an amount greater than 12 atomic percent and less than 35 atomic percent, and “c” represents an amount greater than 0 and less than 30 atomic percent.
It is also known that a ZrO2—In2O3 based protective film for an optical storage medium can be formed by sputtering, by use of a ZrO2—In2O3 based target having substantially the same component compositions as the component compositions of the protective film.
The foregoing technique has been disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2005-56545.
In the conventional method for forming a sputtering target for forming a ZrO2—In2O3 based protective film for an optical storage medium, zirconium oxide powders, indium oxide powders, and powders of the oxidative product of the A which serve as raw material powders, are prepared. The raw material powders are compound and blended with a predetermined percentage, and mixed powders are produced. The mixed powders are baked in an air atmosphere or in an oxidized atmosphere such as an oxygen atmosphere after the mixed powders are produced.
In a conventional target formed in this manner, the large amount of Zr that is included in the conventional target used for forming a ZrO2—In2O3 based protective film for an optical storage medium is a zirconium oxide phase.
The other are compositions made of a indium oxide phase and an oxidative product phase of the A.
However, in the case where a high output sputtering is performed by use of the target used for forming the ZrO2—In2O3 based protective film for an optical storage medium, and the large amount of Zr is a zirconium oxide phase and the other compositions are made of an indium oxide phase and the oxidative product phase of the A in the target, there is a problem in that, a crack is generated in the target during the sputtering, and it is impossible to efficiency form the protective film used for an optical storage medium.